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EUROPROBE PROJECTS
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KIMBERLITE:
Structure and
Evolution of Cratonic Lithospheric Roots |
The Precambrian cratons are characterised by deep lithospheric roots; the
latter are apparent as geoid highs and as positive velocity anomalies in global seismic
tomographic images down to a depth of 200-300 km. These roots are explained by a variety
of hypotheses, ranging from cooling of an old lithosphere to chemical differentiation. EUROPROBE’S
KIMBERLITE project aims at clarifying the origin and evolution of the deep
cratonic lithosphere, combining geochemical and petrological investigation of xenoliths
from kimberlites and basalts with geophysical studies for definition and characterization
of deep structures.
Kimberlites and lamproites seem to be always related to thick Archaean and
Palaeoproterozoic cratonic lithosphere. Their ages are mainly Phanerozoic, but range back
to the Mesoproterozoic, eruptions occurring often in relatively small areas over a long
time span. The magmatic rocks as well as the xenoliths shed light on the mineralogical
composition, fluid content and thermal evolution of the lithosphere and asthenosphere at
depths down to at least 250 km. Geophysical, especially different seismic methods, are
able to define structures in the deep lithosphere, such as shear zones or chemical
layering, which may give clues to the origin of the lithospheric roots and kimberlite
magmatism.
The Yakutian province in Siberia and the Arkhangelsk province in northern Europe are major
kimberlite areas. The former offers an outstanding data base of xenoliths and
exceptionally detailed crustal and uppermost mantle seismic data. The KIMBERLITE
project therefore focuses on studies in this area, exploiting existing and contributing
new data.
Highlights of KIMBERLITE studies include:
Reinvestigation of the detailed seismic images of the crust and upper
mantle, showing azimuth-independent very high velocities (8.8-9.0 km/s).
Exploitation of very long-range seismic profiles sourced by peaceful
nuclear explosions (PNE), giving high resolution information about upper mantle
structures, including the transition zone down to c. 670 km depth, and characterization of
small scale heterogeneities in the scattered wave fields.
Search for anisotropy (both structural and mineralogical) in the upper
mantle, as an indicator of processes in the lithosphere, asthenosphere and deeper levels,
by observation of birefringence of seismic S-waves in broad band recordings.
Study of a large number of diamondiferous kimberlite and lamproite pipes,
which are commercially exploited, ranging in age from 450 to 150 Ma, with numerous crustal
and mantle xenoliths, derived from depths of down to 250 km.
Get the KIMBERLITE text and figures out of the EUROPROBE 1996
publication by clicking on the corresponding text. Click on the figure and see the image
enlarged.
PDF-viewers can be obtained through the net
for different operating systems.
Text (PDF file, 275 kb)
Fig. 11.1.
Distribution of kimberlites and related rocks of the Siberian Platform.
EPS (75 kB)
PDF (30 kB)
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Fig. 11.2.
Map of sub-Moho velocities in the southern part of the Yakutian kimberlite
province.
EPS (190 kB)
PDF (70 kB) |
Note: This EUROPROBE Project is completed.
For more information please contact the project leader:
Dr. Stephan Sobolev
GeoForschungsZentrum Potsdam
D-14473 Potsdam
GERMANY
Tel: +49-331 288 12 48
Fax: +49-331 288 12 66
E-mail: stephan@gfz-potsdam.de
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